Multiple vertical diaphragm type electrolytic cell for producing caustic soda

ABSTRACT

An electrolytic cell for producing caustic soda comprising a large number of unit cells installed compactly in a cathode tank in electrically parallel connection, each of said unit cells consisting of two anode plates interwelded by at least two electroconductive supporting rods which in turn are connected to outer bus bars, an iron mesh cathode frame lined with an asbestos diaphragm surrounding the anode plates at a prescribed narrow distance, a corrosion-resistance cap mounted on the iron mesh cathode frame and a bottom dish inserted thereinto. The outer upper side walls of the anode plates are supported by setscrews to prevent the upper part of the anode plates from rocking.

United States Patent n91 Shibata et a1.

[ May 13,1975

[75] Inventors: Hiroshi Shibata; Yasuo Yamazaki; Yoshikazu Kokubu; Isao Okazaki, all of lwaki, Japan [73] Assignee: Kureha Kagaku Kogyo Kabushiki Kaisha, Tokyo, Japan 221 Filed: Nov. 28, 1973 211 Appl. No; 419,864

[30] Foreign Application Priority Data Dec-'1, 1972 Japan 47-120718 [52] US. Cl. 204/258; 204/253; 204/266; 204/286 [51] Int.Cl B0lk 3/10 [58] Field of Search 204/252, 253, 258, 266, 204/286 [56] References Cited UNITED STATES PATENTS 1,172,932 2/1916 Bucknam 204/258 Allen 204/258 Allen 204/266 X Primary Examiner-John H. Mack Assistant Examiner-W, 1. Solomon Attorney, Agent, or FirmFlynn & Frishauf [57] ABSTRACT An electrolytic cell for producing caustic soda comprising a large number of unit cells installed compactly in a cathode tank in electrically parallel connection, each of said unit cells consisting of two anode plates interwelded by at least two electroconductive supporting rods which in turn are connected to outer bus bars, an iron mesh cathode frame lined with an asbestos diaphragm surrounding the anode plates at a prescribed narrow distance, a corrosion-resistance cap mounted on the iron mesh cathode frame and a bottom dish inserted thereinto, The outer upper side walls of the anode plates are supported by setscrews to prevent the upper part of the anode plates from rocking,

7 Claims, 2 Drawing Figures MULTIPLE VERTICAL DIAPHRAGM TYPE ELECTROLYTIC CELL FOR PRODUCING CAUSTIC SODA This invention relates to an electrolytic cell of vertical diaphragm type for producing caustic soda, and more particularly to a multiple cell constructed by compactly installing a large number of vertical unit cells in a spacious cathode tank in electrically parallel connection.

According to one of the prior art multiple vertical diaphragm type electrolytic cells, a cathode section constructed by a large number ofintegrally combined cathode compartments each surrounded by an iron mesh electrode and diaphragm is disposed between numerous anode plates set up close to each other in a single anode tank. (See U.S. Pat. Nos. 2,742,419 and 2,742,420.) Further according to another known electrolytic cell of the above-mentioned type (See U.S. Pat. No. 1,806,065,), a single and long cathode chamber passes in a zigzag fashion through the interspaces between numerous anode plates set up side by side in an anode tank.

With the aforesaid conventional multiple cells, the anode plate generally has such a large surface area as is defined by a height of 70 to 80 cm and a width of 100 to 200 cm, and moreover the anode and cathode members are spaced from each other at as narrow an interval as 1 cm. Therefore, it is considerably difficult to maintain said narrow interval uniformly throughout the cell. The prior art multiple cells have further disadvantages that concrete or rubber lining used is not sufficiently effective to pervent the inner walls of the anode tank from being corroded by chlorine gas evolved from the anode, necessitating the frequent repair of said inner walls; anode plates, iron mesh cathode frame and diaphragm also have often to be repaired or replaced; a great deal of time and work is consumed in dismantling the integrally arranged anode and cathode members for repair and thereafter reassembling them or replacing defective or worn members of said integral assembly by fresh ones; and great difficulties are encountered in attaining a uniform space between the anode and cathode members throughout the cell, thus making it necessary to maintain the mean cell voltage of one tank at a higher level than 4.0 volts.

It is accordingly an object of this invention to provide a multiple vertical diaphragm type electrolytic cell, wherein a uniform distance can be maintained between the anode and cathode members throughout the cell so as to reduce the mean cell voltage as much as possible from the level which has been required for the prior art electrolytic cell.

Another object of the invention is to provide a multiple vertical diaphragm type electrolytic cell admitting of quick repair.

The above-mentioned objects are attained by an electrolytic cell in accordance with this invention which is characterized in that a large number of unit cells wherein each upright anode plate is spatially surrounded by an iron mesh cathode frame having its inside fitted with a diaphragm are detachably and compactly installed in a big cathode tank in electrically parallel connection, said iron mesh cathode frames being connected to the cathode tank.

Other important objects and advantageous features of this invention will be apparent from the following description and drawings, wherein, for the present purpose of illustration only, specific embodiments of this invention are set forth in detail.

ln the drawings,

FIG. 1 is an elevational cross sectional view on line A-A of a unit cell shown in FlG. 2, concurrently showing the manner in which the unit cell is fitted to a big cathode tank;

and FIG. 2 is a schematic fractional perspective view of a multiple vertical diaphragm type electrolytic cell according to an embodiment of this invention with the cathode tank indicated partly in section,

Referring to FIG. 1, a unit cell 1 consists of a set of two upright titanium anode plates 2 to 3 mm thick, electroplated by, for example, platinum group metal 3; an iron mesh cathode frame 4 lined with an asbestos diaphragm 5 and so disposed as to surround each set of the anode plates 2 at a fixed interval of about 6 mm; a cap 6 made of material resistant to corrosion by chlorine gas and a solution of common salt and fitted into the upper part of said cathode frame 4; and a dish 7 formed of similar corrosion resistant material and in serted into the lower part of said cathode frame 4. The corrosion-resistant material may consist of, for example, rubber, polyvinyl chloride or polyvinylidene fluoride. The peripheral portion 8 of the bottom dish 7 fully covers an iron frame 11. Pressed against the peripheral portion 8 are the lower portions of the diaphragm 5 and iron mesh cathode frame 4 by means of flanges 12, which in turn are fixed to an iron bottom plate 9 by setscrews 13, thereby causing the iron mesh cathode frame 4 to be electrically connected to a big cathode tank 10 (FIG. 2) which is properly connected to a cath ode bus bar not shown in the figure.

The two upright anode plates 2 are interfixed by welding with at least two similarly upright titanium-clad copper rods 14 about 30 mm in diameter. The lower end portion of the copper rod 14 penetrates the iron bottom plate 9, projects downward therefrom and is tightly fixed to a corresponding anode bus bar 16 by bolt-nuts assemblies 17 respectively. A rubber packing tube 19 is inserted into an interstice between a penetrating hole 18 of the bottom dish 7 and iron bottom plate 9 and the outer periphery of the copper rod 14, thereby effecting insulation between the anode and cathode members and also preventing the leakage of anode liquorv In order to maintain the distance between the anode plate and the side wall of cathode frame to be constant, the outer upper side walls of the set of anode plates 2 are supported by a plurality of setscrews 20 electrically insulated and held gastight by a packing 21 so as to prevent the rocking of the upper part of the set of anode plates 2.

Where it is desired to simplify the assembly of the anode plates 2 and copper rod 14, both members may be integrally formed of graphite. Since, however, the graphite material is subject to crumbling while it is molded into said assembly or during operation, a graphite anode member is not favorably accepted in a large scale industrial production of caustic soda.

A large number of unit cells 1 constructed as described above are arranged, as shown in FIG. 2, in the cathode tank 10 at a prescribed interval of I0 mm in electrically parallel connection. The top surface of the cap 6 of the unit cell 1 is penetrated gastightly with a corrosion-resistant fluid pipe 22 through which brine or chlorine gas passes. This fluid pipe 22 passes gastight through the upper lid 23 of the cathode tank to project upward therefrom so as to communicate with a main corrosion-resistant pipe 24 horizontally extending over the cathode tank 10. The main pipe 24 is connected at one end to a brine supplying pipe 25. Connected to the upper side of the main pipe 24 is an upright head pipe 26, the upper end thereof is fitted with a chlorine gas outlet pipe 27. The head pipe 26 is provided with a liquid level indicator (not shown}. The upper lid 23 of the cathode tank 10 is fitted with a hydrogen gas outlet pipe 28, and one side wall 29 of the cathode tank 10 is provided with a caustic soda solution outlet pipe 30 at a point substantially as high as the cap 6 of the unit cell 1.

Brine saturated with common salt is supplied to the main pipe 24 through the inlet pipe 25 and continuously introduced into each unit cell 1 through the fluid pipe 22. The flow rate of brine is controlled by readings on the liquid level indicator. The brine is electrolyzed by impressing a proper amount of voltage across the anode and cathode. Chlorine gas evolved around the anode plates 2 bubbles up through the brine contained in the unit cell 1, fluid pipe 22, main pipe 24 and head pipe 26, and is discharged through the outlet pipe 27 into a chlorine gas holder (not shown). On the other hand, an electrolytically produced caustic soda solution and hydrogen gas collected in the cathode tank are drawn off through the outlet pipes 30 and 28 into a caustic soda solution tank and hydrogen gas holder (not shown) respectively.

The above-mentioned electrolytic cell may be moditied into such type wherein both end faces of the iron mesh cathode frame 4 are replaced by an iron plate coated with corrosion-resistant material so as to be prevented from being used as cathode.

According to still another modification, a single main pipe for conducting concurrently brine and chlorine gas may be replaced by two main pipes for conducting these materials separately.

The subject electrolytic cell may be further modified by reversing the vertical arrangement of the unit cells and anode bus bar from the embodiment of FIG. 1, namely. installing the anode bus bar horizontally above the cathode tank and suspend each set of anode plates therefrom through the upper lid 23. This last men tioned modification is not indicated in the appended drawings.

In the prior art multiple vertical diaphragm type elec trolytic cell, the multiple anode and multiple cathode are respectively integrated into one body, as described in the initial part of this specification. If a part of said anode and cathode assembly is damaged, then the defected body will have to be taken out ofthe anode tank to be replaced by a separately provided flowless body. This replacement consumes a great deal of time and work. Further, repair of the damaged body is accompa nied with considerable difficulties due to the compli cated form of the body. Where a spare body is disposed in the anode tank, it is very difficult to maintain a uniform interval between the iron mesh cathode frame and anode plates throughout the cell.

In contrast, the multiple electrolytic cell of this invention has a large number of unit cells of simple construction separately placed in the cathode tank. Where, therefore, any of the unit cell is damaged, it is only required to open the cathode tank and remove the damaged cell alone for replacement by a spare one, thus quickly finishing reassembly. As apparent from FIG. I, the anode plate and iron mesh cathode frame can be easily kept apart at a fixed interval, minimizing time and work required for repair of the cell. Reliable main tenance of a prescribed narrow space between the anode and cathode members enables an aqueous solution of caustic soda to be electrolytically produced at a prescribed concentration more efficiently with lower cell voltage than in the prior art multiple cell.

To exemplify the advantageous features of this invention, replacement of the anode or cathode body included in the prior art multiple electrolytic cell consumed at least five hours, whereas, with the multiple cell of this invention, replacement of one unit cell included in one cathode tank only took about half an hour. For further illustration with a prior art multiple cell wherein the anode and cathode members were spaced at a mean interval of about 10 mm, a mean cell voltage higher than 4.0 volts was required for produc tion of an aqueous solution of caustic soda at l l percent concentration, whereas, with a multiple cell ac cording to this invention wherein the anode and cath ode members were set apart, for example, at an interval of exactly 6 mm, a mean cell voltage lower than 3.8 volts was only required for said production. In these compared cases, the mode current density stood at about 25 A/dm and the electrolyte bath temperature at about C.

For the initial operation of the multiple cell of this invention, it is desired that power be introduced when the cathode tank is fully filled with brine and the liquid level be gradually lowered with increasing volumes of hydrogen gas evolved by electrolysis, in order to prevent the explosion of the mixture of hydrogen and oxygen gases in the cathode tank. The caustic soda solution outlet pipe 30 should be fitted to the side wall 29 of the cathode tank 10 at such a point as causes the liquid level therein to be maintained substantially as high as the top of the unit cell in normal operation. It is also necessary that the unit cell be always fully filled with brine, and the level of the brine be kept within the head pipe 26.

In the aforementioned exemplifying case, the head difference between the cathode and anode liquor surfaces in the initial operation period was made about 30 cm, and after 6 months, said difference was raised to about cm in order to overcome the increased penetrating resistance of diaphragm.

What we claim is:

l. A multiple vertical diaphragm type electrolytic cell for producing caustic soda comprising:

a plurality of unit cells installed compactly in a cathode tank in electrically parallel connection, each of said unit cells including two anode plates intertixed by welding with at least two electroconductive supporting rods which in turn are connected to outer bus bars respectively,

an iron mesh cathode frame lined with an asbestos diaphragm surrounding the interfixed anode plates at a prescribed distance,

a cap made of corrosion-resistant material mounted on the iron mesh cathode frame,

a bottom dish inserted thereinto, and

means for supporting the outer upper side walls of said anode plates, said supporting means including a plurality of setscrews electrically insulated and held gas tight by a packing so as to prevent the rocking of the upper part of said anode plates.

2. An electrolytic cell according to claim 1, wherein the prescribed distance is about 6 mm.

3. An electrolytic cell according to claim 1, wherein the iron mesh cathode frame is fixed to the bottom plate of the cathode tank by means of flanges and boltnut assemblies.

4. An electrolytic cell according to claim 1, wherein the iron mesh cathode frame has its narrow side walls formed of iron plates and is lined with a corrosionresistant material.

5. An electrolytic cell according to claim 1, wherein the cathode tank has an outlet pipe for an aqueous caustic soda solution.

6. An electrolytic cell according to claim I, wherein each unit cell has a corrosion-resistant pipe for brine and chlorine gas connected to the top of the cap mounted on the iron mesh cathode frame and also to a main pipe horizontally extending over the cathode tank, said main pipe being connected at one end to a brine supplying pipe and on the top side to an upright head pipe fitted with an outlet pipe for chlorine gas.

7. An electrolytic cell according to claim 1, wherein each unit cell has two fluid pipes made of corrosionresistant material and connected to the top of the cap mounted on the iron mesh cathode frame, one of said fluid pipes being used for drawing off the chlorine gas evolved around the anode plates and connected to one main pipe for chlorine gas, and the other for supplying brine to the cell connected to another main pipe for brine. both main pipes horizontally extending over the cathode tank. 

1. A MULTIPLE VERTICAL DIAPHRAGM TYPE ELECTROLYTIC CELL FOR PRODUCING CAUSTIC SODA COMPRISING: A PLURALITY OF UNIT CELLS INSTALLED COMPACTLY IN A CATHODE TANK IN ELECTRICALLY PARALLEL CONNECTION, EACH OF SAID UNIT CELLS INCLUDING TWO ANODE PLATES INTERFIXED BY WELDING WITH AT LEAST TWO ELECTROCONDUCTIVE SUPPORTING RODS WHICH IN TURN ARE CONNECTED TO OUTER BUS BARS RESPECTIVELY, AN IRON MESH CATHODE FRAME LINED WITH AN ASBESTOS DIAPHRAGM SURROUNDING THE INTERFIXED ANODE PLATES AT A PRESCRIBED DISTANCE, A CAP MADE OF CORROSION-RESISTANT MATERIAL MOUNTED ON THE IRON MESH CATHODE FRAME, A BOTTOM DISH INSERTED THEREINTO, AND MEANS FOR SUPPORTING THE OUTER UPPER SIDE WALLS OF SAID ANODE PLATES, SAID SUPPORTING MEANS INCLUDING A PLURALITY OF SETSCREWS ELECTRICALLY INSULATED AND HELD GAS TIGHT BY A PACKING SO AS TO PREVENT THE ROCKING OF THE UPPER PART OF SAID ANODE PLATES.
 2. An electrolytic cell according to claim 1, wherein the prescribed distance is about 6 mm.
 3. An electrolytic cell according to claim 1, wherein the iron mesh cathode frame is fixed to the bottom plate of the cathode tank by means of flanges and bolt-nut assemblies.
 4. An electrolytic cell according to claim 1, wherein the iron mesh cathode frame has its narrow side walls formed of iron plates and is lined with a corrosion-resistant material.
 5. An electrolytic cell according to claim 1, wherein the cathode tank has an outlet pipe for an aqueous caustic soda solution.
 6. An electrolytic cell according to claim 1, wherein each unit cell has a corrosion-resistant pipe for brine and chlorine gas connected to the top of the cap mounted on the iron mesh cathode frame and also to a main pipe horizontally extending over the cathode tank, said main pipe being connected at one end to a brine supplying pipe and on the top side to an upright head pipe fitteD with an outlet pipe for chlorine gas.
 7. An electrolytic cell according to claim 1, wherein each unit cell has two fluid pipes made of corrosion-resistant material and connected to the top of the cap mounted on the iron mesh cathode frame, one of said fluid pipes being used for drawing off the chlorine gas evolved around the anode plates and connected to one main pipe for chlorine gas, and the other for supplying brine to the cell connected to another main pipe for brine, both main pipes horizontally extending over the cathode tank. 